Biopolymers which are biologically derived macromolecules have each specific physical and biological property, and therefore are frequently used for medical and biological use. However, biopolymers are generally inferior in terms of workability and performance control as compared with synthetic polymers, and therefore biopolymers are attempted to be highly functionalized by hybridization of biopolymer and synthetic polymer or chemical modification with low molecular weight compound.
On the other hand, by development of genetic engineering, it becomes possible to artificially synthesize various proteins which are equivalent or similar to biological proteins, as well as novel proteins. In particular, a functional group which can be chemically modified can be introduced into an artificially synthesized protein. By such chemical modification of a novel protein, a protein analogue which is more highly functional can be produced. However, in such procedure, introduction of a functional group into a side chain is limited, and at present there are many functional groups which cannot be introduced.
When a side chain of biopolymer or polypeptide is chemically modified, there is generally used a method by condensation reaction using an amino group or carboxyl group in water. Namely, water soluble biopolymer or polypeptide is dissolved in water, and is reacted with a compound having a desired functional group by a condensing agent, so that a functional group is introduced into biopolymer or polypeptide (Patent document 1). It is difficult to apply this method for the introduction of poorly soluble compound. For the introduction of poorly soluble compound, there is used a method where a compound to be modified is previously dissolved in sodium hydroxide solution, and the pH of the solution is then returned to be around neutral, and the reaction is carried out in water (Non-Patent Document 1). However, it has been suggested that, in this method, high solubility cannot be achieved in the case of highly hydrophobic compound and this method cannot be applied to a compound having a functional group which causes degradation or reaction in the alkaline state.
On the other hand, proteins such as collagen or gelatin are dissolved in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP). Therefore, production of matrix for tissue construction (Patent Document 2) and production of fibrous form matrix by electrospinning (Patent Document 3 and Patent Document 4) is performed. However, these attempts are directed to the production of matrix only, and these documents neither teach nor suggest any chemical modification of protein.    Non-Patent Document 1: Journal of Biomaterial Science, Polymer Edition 16 (7) 809-827, 2005    Patent Document 1: Japanese Patent Publication (Kokai) 2001-224677    Patent Document 2: Japanese Patent Publication (Kohyo) 2002-531182    Patent Document 3: Japanese Patent Publication (Kohyo) 2004-532802    Patent Document 4: Japanese Patent Publication (Kokai) 2004-321484